This application incorporates by reference of Taiwan application Serial No. 90118506, filed Jul. 27, 2001.
1. Field of the Invention
This invention relates in general to a control system. More specifically, the invention relates to a system for controlling the rotational speed of a fan.
2. Description of Related Art
As the technology of the computer progresses, compact and lightweight electronic products, such as the notebook computer, have become the main products in the market. In compact and lightweight electronic products, the products"" ability to dissipate the heat generated usually affects the system stability, product performance, and product durability. For a computer system, in order to quickly dissipate the heat generated by the computer system, a heat dissipation device is usually assembled in the computer system, so that the computer system can work normally in an environment with a suitable temperature.
In a conventional computer system, the fan for dissipating heat is driven by a brushless DC motor. Conventionally, coils with different numbers of turns are assembled on the rotor of the motor to obtain fans meeting different specifications. For example, when a fan with a higher rated rotational speed is required, a coil with a large number of turns can be assembled, and when a fan with a lower rated rotational speed is required, a coil with a small number of turns is assembled. When the current is conducted, coils with different numbers of turns will generate magnetic fields with different strengths, so that the rotational speed of the motor is different and the rotational speed of the fan is changed accordingly.
When fans with different specifications are needed in the market, the provider has to have coils of various types in stock with respect to the number of turns. However, because the provider has to stock various coils, the material cost is increased. On the other hand, for the fans in which the numbers of turns of the coil are the same, the assembly tightness, eccentricity of the fan, difference of inertia of the fan, deviation of the coil shape, and so forth will affect the rotational speed of the fan. The provider needs to spend time to adjust the variable factors, which have influences on the rotational speed of the fan, to comply with the rated rotational speeds defined according to specifications of various types of the fan. Accordingly, the invention is designed to save time and cost, because conventional products must be tested or eliminated if they do not meet the required specifications, which will increase the manufacturing cost and the manufacturing time.
According to the foregoing description, an object of this invention is to provide a system for controlling the rotational speed of a fan, wherein coils with the same number of turns can be used to obtain various rated rotational speeds in fans of different specifications, by altering the reference frequency of the controlling system. Because coils with different number of turns are not required in stock at the same time, the time cost and the manufacturing cost can be reduced.
According to one object of the invention, the invention provides a system for controlling the rotational speed of a fan according to a reference clock having a reference frequency, and the rotational speed corresponds to a fan rotational speed signal. The system comprises a fan rotational speed controlling unit, a voltage generating circuit, and a driving unit. The fan rotational speed controlling unit is used for comparing the reference clock with the fan rotational speed signal, to output a speed control signal. The voltage generating circuit generates a level signal corresponding to the speed control signal. The driving unit generates a driving signal to control the rotational speed of the fan according to the level signal. The fan rotational speed controlling unit includes a reference rotational speed calculating unit for determining a reference rotational speed corresponding to the reference frequency; a fan rotational speed calculating unit for determining a fan rotational speed corresponding to the fan rotational speed signal; and a comparator for producing the speed control signal according to a difference between the reference rotational speed and the fan rotational speed, the speed control signal being indicative of accelerating, decelerating, or maintaining the rotational speed of the fan. The voltage generating circuit includes a charge pump which generates the level signal according to the speed control signal. The voltage generating circuit generates a level signal corresponding to the speed controlling signal. The driving unit generates a driving signal to control the rotational speed of the fan according to the level signal.
According to another object of the invention, the invention provides a system for controlling the rotational speed of a fan, wherein the rotational speed corresponds to a fan rotational speed signal. The system comprises a reference frequency generator, a fan rotational speed controlling unit, a voltage generating circuit, a pulse width modulation (PWM) generating circuit, and a fan driving circuit. The reference frequency generator is used for generating a reference clock having a reference frequency. The fan rotational speed controlling unit compares the reference clock with the fan rotational speed signal to output a speed control signal. The voltage generating circuit receives the speed control signal to obtain a level signal correspondingly. The pulse width modulation (PWM) generating circuit generates a square wave signal according to the level signal. The fan driving circuit receives the square wave signal to generate a driving signal to control the rotational speed of the fan.